Several factors are affecting the dynamics in the treeline ecotone. Both climate, herbivory and changed landuse affect recruitment, mortality and growth in this trasition zone between forest and alpine areas. In addition to that it can be challenging to quantify the effect of each factor, several local factors are in play, such as ground vegetation, micro topography, aspect etc. This master thesis uses multi-temporal observations of trees in the treeline ecotone of 35 sites distributed along a more than 1000 km latitude gradient, to analyze regional differences in recruitment, mortallity and growth. The thesis includes analyses of the effets of climate and herbivory on the changes in the treeline ecotone. The thesis is a part of the project ForestPotential.

A changing climate affects both the growth and the potential extent of our forests. Quantification of the effects is, however, not a trivial task. Climate change involves both changes in temperature and precipitation and studies have predicted that the magnitude of these changes will vary across latitudinal and altitudinal gradients. The competitive relationships between different vegetation species are also likely to change with changes in climate. In the boreal-alpine and boreal-tundra tree line ecotones, the changes are expected to be most rapid, both because trees here to a large degree grow on their tolerance limit in terms of climatic conditions, but also because the number of grazing domestic animals have declined in the last decades. A potential increased forest area because of upwards- and northwards shifts in the tree line will have an effect on carbon sequestration, but also the albedo effect and biodiversity in the tree line ecotone. Even for the forests well below the tree line, the growth conditions will change with changes in climate. Increased productivity will have impact both on the climate mitigation potential of the forest sector as well as the sector’s economic potential.

By means of time series data of the growth of trees, both on the productive forest land and in the tree line ecotone, coupled with time series data of climate, herbivory, airborne laser scanning, imagery, and multi-spectral information, the project ForestPotential aims at answering the several important research questions. What are the relative importance of grazing and climate on recruitment and growth in the tree line ecotone, and how accurately can changes be monitored using remotely sensed data? Can bi-temporal airborne laser scanner data be used to accurately estimate forest productivity? With input from the analyses of these research questions, we will also carry out long-term, large-scale forecasts of the Norwegian forest sector, also accounting for the albedo effect and the dynamics of the forest soil carbon stocks.